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Wednesday, July 22, 2015

Roberts R300 Reinvention

Liz: today’s guest post comes from Gordon at IQAudIO, who makes and sells audio accessories for the Pi, which we really, really like – with one of his DACs you can turn your Pi into a proper audiophile-approved piece of kit. Gordon had made a project we really liked the look (and sound) of when we last saw him, so I asked him to write it up. Over to Gordon:

When my grandmother passed away many years ago I was asked if there was anything of hers I'd like to have in order to remember her by. The choice at the time was pretty easy for me – her bright red Roberts radio. This radio sat on her kitchen worktop, and whenever we visited I was always being told off for touching it, tuning it to some other radio station and spinning the whole thing around on its turntable base far too quickly.

The radio, somewhat the worse for wear.

My grandmother was affectionately called "Granny Hi-Tech", simply because she was always the first to get hold of gadgets, most of which I assume she bought having seen them being demonstrated at the large department store in Glasgow where she worked during the 1960's and 70's.

The original intention on receiving the Roberts radio was to get it working again and keep everything authentic, but I really didn't know where to start, so it was placed in a box and forgotten about. It's moved house with us six times since, and was rediscovered, grubby and broken, during our last house move eight months ago.

A bit of a state

I did finally find a spare wet afternoon, but on taking the radio from the box and giving it a good look over, it was obvious I'd been seeing it through rose tinted glasses – it was much worse than expected, and although I may have been able to restore the inner workings, what stations can you pick up on Long and Medium Wave these days?

It was decided that a sympathetic transplant was called for, keeping the aesthetics of the original radio but delivering a modern music playback solution. Some parts of the radio were okay, some terrible and overall it had lost that lovely red colour that I fondly remembered. One of the dials had lost its brass cover, the grill was dented, the Roberts logo was yellow and broken, and the inside had corrosion in places.

A Roberts R300 with Airplay

I could have bought a cheap bluetooth speaker and transplanted the workings into the R300, but I wanted the original radio buttons to work as expected (on/off, volume) and wanted it to have some real musicality to surprise. I also wanted the ability to have synchronous playback across the house with my other HiFi systems. Overall it should look and feel like an original Vintage 1960s radio but in terms of audio performance I wanted it to sound awesome.

Enter the Raspberry Pi

There are several add-on boards for the Raspberry Pi, and we develop and sell a few of these ourselves. For this transplant I used our Pi-DigiAMP+. This Raspberry Pi HAT board takes the digital audio signals (I2S) from the Pi's 40-way header, and delivers high-quality stereo audio up to 192MHz/24bit resolution – you just need to add speakers and a suitable power input to complete the job. The DigiAMP+ is designed to drive bookshelf or larger speakers – we usually pair it with QAcoustics 2010i or 3020 speakers, and it sounds simply brilliant. We demonstrated this very combination at the recent CamJam and also at the Recursion Computer show in Stratford-Upon-Avon.

The IQaudIO Pi-DigiAMP+ can run from 5v -> 18v, and has on-board circuitry to power the Raspberry Pi too. Here we have used a 15v/3.3amp power brick from XP Power – this will allow the Pi-DigiAMP+ to deliver 2x20watts into 4ohm speakers, with a little less into 8ohm drive units – more than enough for a bedroom or kitchen radio.

Using the Raspberry Pi allows us to take advantage of the many Linux-based music playback solutions available. We could have gone for Volumio, RuneAudio, Moode, PiCorePlayer, Pi MusicBox, Max2Play or others; but for this build we went with Mike Brady's Shairport Sync. Mike is a computer science lecturer at Trinity College Dublin and has posted his source code on GitHub making it easy to build and modify if needed. We've been running Raspberry Pi-based Shairport Sync systems for a while with great reliability and ease of use. Thanks Mike!

Remove the unnecessary and rework the rest

Taking the radio to pieces was pretty simple; there were none of those annoying plastic clips you break when attempting to open a modern device. Here it's mostly wood screws with the occasional brass nut and bolt. We carefully removed the innards and stripped down the radio to its bare components, unsoldered the 60s electronics and removed protruding and unnecessary metal that would make the overall transition more difficult.

Obviously, a 40-year-old paper mono speaker wasn't going to cut the mustard, so we removed that too, replacing it with a pair (to give us both left and right channels) of full range Balanced Mode Radiator (BMRs) drive units – not only do these fit in the available space, but they sound good too.

Now left with a bare carcass, it needed a good old clean and polish, but what we didn't expect was for the carrying handle's leather strap to disintegrate, which was one of the key aesthetics, along with the base turntable, we really wanted to keep. A quick Google search and subsequent calls to Roberts themselves resulted in some replacement (but modern) parts being received next day, although we ended up only using the new silver "Roberts" logo, as the beautiful replacement red handle was just too big a colour difference.

Rebuilding the radio was just like a Haynes manual (refitting is the reverse sequence to removal). We cut an MDF support panel for the speaker drive units.

The analog volume potentiometer of the original was replaced with a simple 3-pin rotary encoder, wired to the Pi's GPIO. We used the sample code from the IQaudio GitHub repository to take the Rotary Encoder pulses and convert them into Linux ALSA volume commands.

From the outside you wouldn't know anything had changed, and to keep the functionality of the radio's Off/Long Wave/Medium Wave selector, we wired it in-line to the positive power from the external power brick. Selecting either Long Wave or Medium Wave powers the Pi-DigiAMP+ and Pi, while selecting Off cuts the power to both – we added a simple power barrel connector onto the back of the radio so it wasn't always tethered and didn’t have a flying lead.

Finally, we replaced the wooden wedges and measured up the display window (ordering another to be laser-cut from www.podbox.co.uk at the same time). We also added some sound damping from an old speaker we had lying around. The handle was repaired using some similar covered vinyl.

As with all good builds, there were a few extra pieces left over…

How does it sound?

Surprisingly good, way better than expected. It really makes us smile streaming Deezer/Apple Music to radio that’s nearly half a century old. Having the physical volume control just adds an extra retro feel too.

What's left to do?

Having used the Raspberry Pi/IQaudio Radio for a while now, we've decided there are a few additional tweaks to perform when we find the time. These include:

Tuning Knob: We need to make the tuning dial do something. This may end up driving some RGB LEDs, delivering mood lighting OR capturing the dial's position (via ADC), and converting that into one of several fixed radio streams, selecting each in turn simply by "re-tuning."

Power LED: Although we do tend to leave the radio powered up permanently, it would be good to know if the kids have turned it off rather than the toaster.

The radio's handle/strap needs work and this is where we'll likely take the modern replacement purchased from Roberts Radio and re-colour it to match the original radio's dulled finish. We've even found a shop called RevivedRadios on Etsy who can recover the Roberts radio in your chosen fabric. [Liz interjects – goddammit, I wish I hadn’t clicked that link. I really want one of those now.]

Better WiFi signal: Although we've got good range already with the Official USB dongle placed in the radio's enclosure, it may be worth exposing the Raspberry Pi's USB socket on the back of the radio case (for better signal reception) along with the Ethernet socket, allowing for direct network connection in suitable locations.

EQ/Bass boost: We could look at diving into the Pi-DigiAMP+'s integrated DSP and program it to get the best from the BMR drive units in the Roberts Radio case.

Battery operation: I’m thinking of adding a battery power source and charging circuit. It's just too nice a radio to have it tied to a mains socket – it also stops me being able to spin the radio around and around listening to music as I did 40 years ago!